Treatment of polymer substances



Paientet i Apr. t, l-t

UNITED l by means assignments, to .lascc, incorporated,

\ a corporation oi l'louisiana lilo Application meoclinher list, lllliil, Serial No, tllilfibil (oi. est es) l large majority of rubberproducts are finally vulll @lalrn.

Thislnvention relates to synthetic polymer materials prepared by thepolymerization of olefin substances such as isobutylene, and relatesparticularly 'to the compounding of the high molecular weight rubberypolymers of the isooleflnes with other substances. More particularly, itrelates to the methods and apparatus for the treatment of the polymerafter the polyrnerization step, with a minimum of clepolymerization ofthe completed polymer.

This application is a continuation in part of my application Serial No.2.372%, filed October 27, 11938.

It has been found possible to polymerize the gaseous iso-olefillesubstances oi the type oi isobutylene into high moleculanweieht polymersto produce synthetic materials of highly viscous or rubbery character.These materials may molecular weights ranging from less than L000 to350,000 or more, and their physical properties vary from those of ahighly viscous oil to those of a rubbery solid, according to themolecular weight.

These materials are useful for many purposes, both in the form asprepared, in the purified form, and in combination with many othersubstances such as oils, fillers,'pigrnents, gums, resins, etc, and thisis particularly the case t1itl1'tl1g,l1igh molecular weight rubberyforms of the polymer.

The iscbutylene polymer material as prepared, especially when theaverage molecular weight isof the order of 50,000 to 350,000, is asubstances having some physical properties much like those of rubber,thatis, the polymer material. is highly elastic like rubber, withsimilar properties of return to shape after deformation, anti similarhigh strength in tension and. compression. lsobutylene polymer substanceis very greatly different from rubber in other respects; for example,the polymer substance is chemically nearly fully saturated, in contrastto the high degree of uneatura tion of rubber; the polymer substance ishighly resistant to oxidation, in contrast to rubber, which. oxidizesreadily; the polymer substance does not vulcanize with sulphur as doesrubber, and sol phur can be combined chemically with the polymersubstance only with great diihcuity and under very special conditions.

Lik rubber, the isobutyleoepolymer is subject to a substantial molecularweight breakdown when worked up on rolls and similar familiar rub bercompounding equipment, and the polymer is much more sensitive to heatdecomposition than is rubber. This characteristic has not causecl anyserious dlfiicuity with rubber because canized, which process appears toinvolve a polymerization reaction, but the isobutylene polymers must heused Without vulcanization and any breakdown or loss or molecular weightwhich once occurs cannot be regained.

I For these reasons, the working up, compound- .ing ancl processing oipolybutylene products of high molecular Weight cannot use the familiarrubber techi'lluue, except in the relatively few cases where breakdownis of no significance, and it is a problem of the first importance todevelop a technique for handling the new polymers with a minimum loss ofmolecular weight.

Working up or compounding the polymer consists in rapidly exposing freshsurfaces of the mass to the treating agent or ctunpouncling ma terlal,but this cannot be done successfully by any process in which thesubjection of the material to pressure, for example, by rolls orsqueezing mechahism, occurs. has been found, however, that compoundingor working can be accomplished very readily by means of various millingmachines which operate on what may be described as a tension principle,that is to say, which effect the continual exposure or" new surfaces bya process of stretching the oi polymer repeatedly. Such working ispracticed in certain remote arts. for example, in breast-making, but isnot used in worlons or CDElipOtlllliiillfi rubber or other similarmaterials.

Rubber can thus be worlrecl on rolls for, the incorporation of pigmentsand other compounding substances with little or no injury to the rubber;whereas the polymer substance isvery sensitive to working upon therolls, and even a few minutes of pressm'e working upon the roll millproduces a great breakdown in molecular weight of the polymer so as todestroy the usefulness of the material for some purposes. and accordingly it has been found impossibl to handle the material in themanner in which rubber is handled, and at the stone timepreserve itagainst this type of rleteri tiou.

The present .ventiontlepends upon the discovery that the Wemer antiPtleiderer type of machine, by which is meant a machine which ftv s thesubstance by a pulling action anti a use ion effect, in a manneranalogous to the pulling of telly (which machine is useless for "millingrubber, because of. the very great surface exposed to air, and theresulting serious oxidation, and the ziihlculty of main the rubberrespond to the movements of the yes) is highly ehlcient and satisfactoryfor use with the polymer material. This high efficiency and usefulnessappear to depend upon the newly discovered fact that whereas pressuredestroys the molecules of the polymer very rapidly, tractive or pullingtreatment has little or no effect in breaking down the polymermolecules.

Furthermore, the polymer substance is much more sensitive to heat, thanis rubber, and an amount of heat which is not only harmless to rubberbut also is necessary to soften it, is seriously harmful to theisobutylene polymer material. 'I'he usual rubber mills such as the rolltype, or the Banbury mixer type, develop large amounts of heat in thebody of the rubber, in consequence of the severe mechanical pressure andinternal friction, whereas the Werner and Pfleiderer type of kneader, byproducing traction only upon the polymer, causes the development of onlya small amount of internal heat, an amount sufficiently small to besubstantially harmless to the polymer material.

To describe the type of action referred to above, applicant uses theword kneading and limits it to the process of continually pulling andstretching the material, as distinguished from the term milling in whichthe compounding or working is accomplished by compression.

There appear to be no necessity of describing in detail the type ofmechanism used for the present process, it being understood thatautomatic taify pulling equipment in which two or more sets of arms areemployed continually stretching out the mass of polymer alternately andallowing it to be folded on itself between the stretching operations, oreven better, mechanism of the same general type used in bread kneading,which is employed to prevent squeezing out of the gas, and not to aprocess analogous to thepresent operation. Bread kneading machinerygenerally consists of a mixing chamber with pairs of rotating armsgenerally set at right angles to each other, with the result that thearms never approach each other so closely as to exert any substantialpressure, but produce a separating and stretching effect on the materialwhich adheres to the arms. A typical machine of this type is theWerner-Pfleiderer kneader which is very satisfactory for the presentpurposes.

The butylene polymer is suiiiciently tacky (th heavy high molecularweight product should be heated mildly) to adhere to the kneading .armsand'is thus repeatedly stretched, folded and :restretched rapidlyexposing new surface to the action of the treating agent or compoundingmaterial. In this manner, the mixing or compounding may be accomplishedin a few hours without substantial breakdown. There is ordinarilysomeloss of molecular weight, but milling for the same time at sametemperature will inevitably produce a much greater deterioration.

Thus, an object of the invention'is to compound an oleflne with othersubstances with minimum reduction of average molecular weight.

In practicing the present invention, the polymer may be prepared by apolymerization procedure which consists in treating the gaseous olefinessuch as isobutylene with a catalyst, such as boron trifluoride, BFa, oraluminum chloride, AlCla, at low temperaturea ranging from --10 C.downto -100 0., preferably in the presence of a suitable solvent such as.a liquefied normally gaseous solvent, say ethylene or ethane or propaneor carbon tetrachloride or carbon disulfide.

In this procedure, it is found that the molecular weight, and with itthe character, and degree of solidity of the material, depend upon thetemperature at which the polymerization occurs, the lower thetemperature, the higher the molecular weight and the more rubbery thepolymer, and on the purity of the iso-olefin polymerized.

The polymer as so prepared should first be freed from the solvent andthis may be accomplished during a kneading operation, the temperature isgradually allowed to rise to room temperature and the gas-free productwashed with water or soda to remove traces of catalyst. Both of theseoperations may be conducted during the kneading step.

Example 1 A batch of the polymer, which may conveniently be an amount of200 pounds, was placed in the Werner-Pfleidere kneader and thekneadingoperation begun for the incorporation of sufficient oil to produce acompound containing 20% of the polymer in the oil. However, the oil wasnot added in total quantity at the beginning of the kneading operation,but the addition of the oil was started in practically a drop-wisemanner, approximately 1 to 3 gallons of oil being added during the firsthour of kneading. If the oil is added at a rate faster than this, thesurface of the polymer becomes coated with a continuous film of oil, andthe oil is no longer mixed in satisfactorily. Instead, the final productwill have in it particles of the original polymer containing no oil.After about 3 to 10 hours, a sufficient amount of oil, that is,approximately 10 gallons, had been added to the 200 pounds ofpolyisobutylene; and a sumcient softening and permeation of thepolyisobutylene.

by the oil was obtained so that the rate of the addition of the oil wasspeeded up considerably. By the time the 10 gallons of oil had beenadded, a considerable change in the polymer occurred and it assumed ataffy-like consistency and the further amounts of oil were worked inmuch more rapidly, the remaining quantity. of the oil being convenientlyadded over the remainder of a time interval of approximately 18 hours,more or less.

Starting with a polymer having an average molecular weight of 150,000,the molecular weight is broken down by the kneading operation no furtherthan to about 110,000, even though the kneading operation is prolonged.In contrast, a similar compounding for a much shorter time for theincorporation of a much smaller amount of oil upon the ordinary rubberroll mills caused a breakdown of molecular weight from 150,000 to64,000, which for many purposes is prohibitively low. 7

A similar procedure may be utilized for the incorporation into thepolymer of pigment and filler substances. Such substances as talc,powdered slate, lime; chalk, asbestos, wood flour. paper fibers, and infact, substantially any of the filler substances may readily beincorporated room temperature, or above room temperature I up totemperatures of about ISO- C. However, for most purposes, where oil isto be incorporated into the polymer, it is preferable to open.

ate at or near room temperature. It is found that operating at roomtemperature, there is less breakdown of molecular weight values of thepolymer than occurs when operations are conducted at highertemperatures. Conversely, at sub-normal temperatures, there is stillless molecular weight breakdown, from temperature,

but the incorporation of the oily material is very much slower, and thegreatly prolonged kneading required result in somewhat more breakdown atsub-normal temperatures, for the incorporation of a given amount of oilinto the polymer, than occurs at room temperature. Similarly, theincorporation of oil is so much more rapid at elevated temperature thatthe very substantial shortening of the kneading operation at elevatedtemperatures results in much less breakdown in molecular weight thanwould occur if the incorporation required the same length of time as atroom temperature. Thus, relatively little difference in product isobtained whether the operation is conducted at sub-normal temperatures,normal temperatures, or elevated temperatures, although at elevatedtemperatures above about 125 C. the temperature breakdown increases withrising temperature more rapidly than does the speed of incorporation ofthe oil into the polymer; hence, a composition prepared at such elevatedtemperatures tends to be of somewhat lower molecular weight than oneprepared at normal temperatures or sub-normal temperatures.

In some instances, however, a substantially elevated temperature isessential to satisfactory mixing, as is the case when paraflin wax is tobe incorporated into the polymer.

Example 2 The Werner and Pileiderer type kneader was heated to atemperature of approximately 93 C. by the use of steam in a steamjacket. Approximately 200 pounds of the polymer were placed in thekneader and the kneading operation begun. Approximately 800 pounds ofparaffin wax of any desired grade, such as wax melting as low as 125 F.to wax melting as high as 145 F., were melted at a convenienttemperature, and the melted wax added to the polymer in the kneadingoperation in-the same manner as disclosed in Example 1, the paraffinbeing added in practically a dropwise manner, although at asubstantially more rapid rate than in Example 1, 7 to pounds of meltedparaffin wax being added in the course of 20 to 40 minutes. At the endof this period, the rate of addition of the melted paraffin wax wasincreased, so that approximately '75 pounds were added in a total timeof 'from 1 to 2 hours. The addition of such an amount of the meltedparaffin is sufiicient to effect a very substantial softening of thepolymer, and permit a much more rapid addition of the melted wax. Theremainder of the 800 pounds of wax was then added at a relatively rapidrate of speed, the overall operation requiring only from 4 to 6 hoursfor the entire mixing procedure.

As in the case of Example 1, polymeric material having a molecularweight or 150,000 to 175,000. may be mixed with the paraflin wax inlarge proportions during which operation the breakdown in -molecularweight of the polymer may be limited to such an amount that at the closeof the compounding;operation, the polymer still has a molecularweightranging from 110,000 to 135,000.

This material when cooled to room temperature is particularly valuablefor a wide range of coating uses, waterproofing and similar uses. As inExample 1, the material may be used as originally compound-ed, or it maybe used in combination with a wide range of pigment and fillersubstances as hereinabove listed.

Example 3 A batch of the polymer having an average molecular weight of100,000 to 150,000 may be placed in the kneader, together with a desiredamount of filler or pigment, which may be from 10 pounds of filler orpigment to 100 pounds of polymer, or lesser amounts of polymer andlarger amounts of filler and pigment may be used, until a proportionsuch as 5 pounds of polymer to pounds of pigment or filler may be used.Over the entire range, the polymer and pigment may be put into thekneader together, the kneading operation started, and continued for alength of time of from 2 to 6 hours. If the proportion of polymer is inexcess of the proportion of pigment,

the operation may conveniently be conducted at room temperature. If,however, the proportion of filler or pigment is greater than theproportion of polymer, the incorporation into the polymer is facilitatedby applying heat to the jacket of the kneading machine. It will be notedthat the amount of kneading required for the incorporation into thepolymer of the solid materials is considerably less, than is requiredfor the incorporation of oily materials, and accordingly the breakdownwhich occurs is considerably less than that which occurs in theincorporation of the oils.

This is in contrast to the situation which obtains either with therubber mill rolls or the Banbury mixer where a longer time, and moresevere working is required for the incorporation of pigment, than isrequired for the incorporation of oily liquids. Accordingly, an attemptto incorporate the solid pigments and fillers on the rubber rolls or inthe Banbury mixer results in much greater and more seriousdepolymerization and reduction of the molecular weight 01 the polymer.

The polymer in some instances contains undcsired impurities, such asacid bodies, traces of the boron trifluoride catalyst, traces of solventfrom the polymerization step, and traces of low molecular weightmaterial. These undesired components are readily removed by a similarkneading procedure in the presence of substantial quantities of water.The type of washing procedure varies according to the molecular weightof the polymer. If the average molecular weight is below 50,000, thewashing operation is relatively simple, since the polymer is lessrubbery, and to some extent approaches a plastic substance.

Example 4 A batch of the polymer material, say pounds, having amolecular weight of 25,000 to 50,000, may be placed in the kneader, andcovered with water. A kneading in water for a period of from 1 to 6hours is suflicient to remove substantially all impurities. It may benoted that with such low molecular weight polymer, there seems to be asmallzquantity of some substance present in the polymer which serves asan emulsifying agent and arr'emulsion of the-polymer in water isproduced rather quickly. ii'he dispersion of the substances into theemulsion form produces a very large surface interface,

through which the water-soluble impurities diffuse very rapidly. Theemulsion may then be broken by heating the kneader, and the water maythen be poured on from the polymer leaving it in pure form free from thevarious abovementioned impurities. An amount of water as small as 10% ofthe amount of the polymer may under these conditions be sufiicient for awashing operation, but for complete removal of impurities, largeramounts are sometime desirable. It may be observed that in thisoperation, practically no breakdown of the polymer occurs.

In the case of polymer having a molecular weight in excess of 50,000,the rubbery character of the polymer makes a washing operation somewhatless easy.

Example 5 Accordingly, the batch of polymer having a molecular weight of55,000 to 350,000 may be placed in the kneader, with approximately ofits weight of water and the kneading started. At the beginning of thekneading, operation, the solid polymer is merely pushed about by thekneading members, but after a time as the kneading proceeds, the polymertakes on a tafiy-like character, and is pulled, stretched and kneadedbetween the blades of the kneading machine. This kneading may becontinued for a period of approximately an hour, at the nd of which timemost of the water will be distributed through the mass of the polymer.Additional water may then be added, in an amount ranging from 10% to100% of the amount of polymer, and the kneading continued for anotherhour, after which. the excess water may be poured oh and replaced withfresh water and the kneading continued for an-- other hour. Theprocedure of kneading the polymer in fresh charges of wash water isdesirably repeated about six times, at the end of which operation thepolymer is substantially free from impurities. As in Example 4, thematerial in the kneader may be heated to break the emulsion, the waterdrawn oil and the material further heated until it is fully dried andfree from impurities" It is to be noted that usually the water forms anemulsion within the polymer with water droplets, as the disperse phase,within the mass of the polymer as the continuous phase, the whole beingsubmerged in a body of water in the i kneader.

A suitable number of changes of water, with adequate kneading in eachchange, will cause the polymer to become neutral to litmus paper, toCongo red paper or to methyl orange solution, and the material becomestasteless and odorless.

The washing and kneading operations are desirably conducted at ordinaryroom temperature, or between 40 and 90 F., since it is found that belowabout 40 F., the emulsion is broken and washing does not occur, andabove 90 the emulsion also is broken and the washing does not occur.

At the completion of the washing operation, the residual water presentin the polymer may be removed by heating the polymer above about F.,whereupon the emulsion is broken, the water is readily removed, and thepolymer returned to its original solid state.

In other instances it is found desirable to incorporate into theisobutylene polymer substance various amounts of gummy materials, orother resins both synthetic and natural, or natural rubber.

Example 6 For this purpose the desired amount of the polymer substancemay be placed in the kneader and the kneading begun, either at roomtemperature, or at somewhat elevated temperatures as desired. Part orall of the gums, resins or rubber may then be added to the kneader andthe kneading continued. Usually it is preferable to knead the polymeralone for a short period of time until the ,tafiy-like state begins tobe assumed. The addition of the gummy, resinous or rubbery materials maythen occur, in some instances the whole amount of gums, resins orrubbery material may be added directly, especially if the amount isrelatively small. Alternatively, the added substances may be put intothe kneader in relatively small portions, with intervals betweenadditions sufficient to permit of the incorporation of a substantialamount of the first poi.- tion before the second portion is added, andthe kneading may be continued until a substantially homogeneous mass isobtained.

Thus the procedure of this invention provides a simple and convenientstep for the processing of the high molecular weight rubbery polymerwhich results in a thorough incorporation of ma-' terial into thepolymer with a minimum of breakdown of molecular weight.

While there are above disclosed but a limited number of embodiments ofinventive concept, it is possible to provide still other embodimentswithout departure from the inventive concept hereinabove disclosed, andit is therefore desired that only such limtiations be imposed upon theappended claims as are stated therein or required by the prior art.

I claim:

In the preparation of a composition of matter comprising apolyisobutylene having a molecular weight between 50,000 and 350,000with a paraffin wax, the step of kneading the paraffin into the polymerat a temperature between the melting point of the paraflin and C., insuccessive small portions, avoiding the formation of slippery surfacelayers by beginning the addition of the molten paraffin in practically adropwise manner, continuing the kneading until the successive portionsare homogeneously incorporated into the polymer, 7 to 25 parts of meltedparafiin per 200 parts of polymer being added in the first 20 to 40minutes.

LUTHER B. TURNER.

